High speed, high intensity optical recording system



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HIGH SIEED.- HIGH :INTENSITY OPPICAL RECORDIEG SYSTEH 3 Shasta-Shui. 3

Filed 09%,. 2E, 1952 :M r x, w j f W2. l AN. @f

Y 3,l54,37 l e illGH SPEED. HEGH lNTENSlTY Pl'lCAL illClliDlNG SYSM Wayne R. `oirnso'n, lLos Angeles, Calif., assigner to With ston Research {Iorporatiomos Angeles, Calif., a cerporation of California Filedct. 26, 1962, Ser. No. 233,249 Claims. (Cl. 3546-408) The present invention relates to optical recording sys-l tems and apparatus, and it relatesvmore particularly to an improved optical recording system for the high speed/ high intensity recordingcf signals extending'through a wide range of frequencies.

The limited intensity of the light sources previously available for opticalrecording systems has meant that the prior art type of optical recording system has relatively limited utility. However, the recent advent of the laser light source has made the provision ot' high speed/high density optical recording systems possible. and `feasible.

Lasers have been operated successfully since i960. The laser, or optical maser as it is sometimes called, amplies light and radiates the amplified light in the form of a coherent, extremely high intensity lightv beam. A description of the laser may be lfound, for example, in the Encyclopedia or Electronics, Susskind, published i962, hy the Reinhold Publishing Company.

An object of the present invention vis to provide an improved high density optical recording system which utilizes a high intensity iight source, such as a laser,.and in which a scanning recording/reproducing light beam from the source is focused to an extremely small spot size on the recording medium storage of the recording signals, or for the proper reproduction of such recorded signals.

Another object is to provide such an improved high density optical recording system in which unique controls are provided to maintain the scanning iight beam in a sharply focused condition on the recording medium in the presence of variations in ambient conditions.

Yet another object is to provide such an improved high density optical recording system in which unique controls are provided to assure proper registry of a scanning light beanrwith recordings on the recording medium for the proper reproduction of such recordings.

A still further object is to provide such an improvedr FIGURE 2 is an enlarged view of the recording photo- I graphic lilm strip, and illustrating the manner in which the light beam is focused to a sharp point in the planeet' the tilin strip and below its photo-sensitive emulsion surface;

FIGURE 3 is a schematic representation of additional components for the recording of FIGURE l which enable particular edge recordings to be made on the film strip for control purposes, as will be described:

FIGURE 4 illustrates a fragment of a tlm` strip bearrecorclngs formed thereon 'cy thecomposite system of FIGURES l'and 3; and

FIGURE 5 is a schematic representation of an optical system for reproducing the information recorded on a tilm strip by the recording system o FIGURES 1 and 3.

t l@ sassari Part-sita occa?, less The improved optical recording system to be described is espcially advantageous in that extremely, high storage density of the recorded signals may be achieved. This is possible because the high intensity light sourcebf the system produces a coherent iight beam which may be focused to an extremely small spot-entire surface of the recording medium. v

Also, 'the high intensity light source of the system of the invention permits the recording to be carried out atan extremely high speed so that the system is capableof recording and storing signals through a wide frequency band. For example, video signals extending from (l to 2O megacycles may be .conveniently recorded-by the optical recording system of the invention. l

The optical'recording system shown schematically in FIGURE l includes a laser light source The laser light sources produces a coherent high intensity light beam along a particular path. A'rotatable reflecting member 12 is disposed in the light path ci the laserlight beam, and this reflecting member is rotatably driven, so that the beam may-be rellected and scanned transversely acressa recording lm strip id. v l

The film strip 1d is supported on a platen 16', and is moved across the platen in FIGURE l in a direction perpendicular to the plane of the paper'. The rotatable movement or" the retiecting member 12 causes the light beam to be recurrently scanned transversely across the lm strip 1d, as the lm strip is drawn along its particular path.

A lens 1S is interposed in the path-of the laser light. beam between the light source 1!) and the rotatable reilecting member i2. This lens causes the light beam to ber'ocused toa sharp pointtFiGURE 2) beneath the surface of the photo-sensitive emulsion coating on the recording medium id. The recording medium 34 may, for example, be formed of an optical grade transparent Mylar base. The photo-sensitive emulsion is formed on the base, and the density ofthe emulsion is varied in accordance with the modulations `on the laser iight beam which is transversely' scanned across the recording medium. i

The laser iight beam fromfthe source 1li! is intensity modulated by a suitable light modulator 19. lThe light modulator i9 is disposed in the path oi the laser light beam between the sourced!) and the lens 18. A source 20 of video signals, for example, is .coupled io the light modulator 19. These signals may, for example, extend through a frequency range of from t) to 20 megacycles, and they cause the light modulator 19 toV intensity modulate the laser light beam. Light modulators which respond to applied electrical signals to intensity-modulate a light beam are well known. For that reason, it is'believer that a detaileddescripti'on of the modulator 19 is unnecessary herein. 'i v .The platen 16 is coupled to a manifold 22 which, in turn.' is coupled to an .appropriate vacuum pressure source. The construction is such that a vacuum pressure is exerted at the surface of the platen i6 to hold the recording iilm strip i4 securely in the piane ot" its particular path. The platen 16 is curved, as shown, to correct for geometric distortions of the scanning beam due to the rotation of the reflecting member i2. rl`his enables the beam to he maintained focused at a point at a particular level in the photo emulsion shown in FIGURE 2. The surface of the platen i6 is optically ground and lapped to a smooth arcuate configuration.

The rotating reflecting member 12 has a polygonal peripheral surface. as illustrated, and it may he rotated at an extremely high speed to produce corresponding high speed cyclic scanning of the light-beam across the recording medium. The rotating reflectingmember 12 may be constructed, for example, in the manner described in an article at page 134 of the April. 196i edition of Scientific American. The polygonal faces ot the reflecting nicmber 12 are optically ground in the usual precise manner to exhibit planar surfaces.

It is most important in the practice of the invention that the laser light beam from the source .10 be focused to a point at a particular level in the photo-sensitive emulsion layer of FGURE 2. However, the recording nlm strip 1d is subject to thickness variations upon changes in ambient conditions of temperature and humidity. To compensate for such ambient changes, a micrometer control 26 is coupled to the platen 16. This micrometer control may have any known construction, and it responds to an electrical control signal to move the platen 16 through a minute displacement towards and away from the rotatable reflecting member-12. v

As an alternative, a micrometer position control 28 of any known construction is coupled to the lens 18. This latter micrometer control responds to an applied electrical signal to shift the lens slightly towards or away from the reflecting member 12, so as to control the focus point in FGURE 2.

A temperature/humidity 'sensitive sensing element 3G is positioned adjacent `the platen 16. The element 30 responds to changes in the ambient conditions in the vicinity of the platen 16, and it applies corresponding electrical signals to a control unit 32.

The control unit 32 applies control signals to the micrometer position control 26 and/or to the micrometer position control 28. These control signals cause the control 26 to move the platen 16 slightly towards or away from the rotatable reflector 12 in response to changes in ambient conditions, as sensed by the'element 3l). These ambient changes produce corresponding changes in the thickness of the lilrn strip 14, so that the controlled shifts of the platen 16 maintains the upper surface of the hlm strip 14 in the plane of its particular path.

As :an-alternative to the control described in the preceding paragraph, or in conjunction therewith, the slight shift in the position of the lens 18 under the control of the position control 28 causes the focus point of the light beam from the reflecting member 12 to be maintained at the desired level in the photosensitive emulsion regardless of thickness variations of the lm strip 14.

As noted above, the system of FIGURE 3 includes addii tional components for the recording system of FIGURE 1 to enable certain edge recordings to be made on the film strip .14. Certain of the components previously described in FIGURE l have been omitted from the system of FIGURE 3 for purposes of clarity.

-V 4... s "the polygonal reflecting faces ol the reflector member `l2. The synchronizing pulses from the sensor 56 are amplified VAin an amplifier 58 and applied to the light modulator 38.

In the system of FIGURE 3, a half-silvered mirror 36 is disposed lin 'the pathof the laser light beam betweenthe source 10 and the light modulator 19. This 'halfsilvered mirror 36 permits the major portion of'the laser light beam to pass through the modulator 19 and through the lens 18 to the rotatable reflector 12. However, a portion of the light beam is reflected by the reflector 19 down through an additional light modulator 38, and through an `:appropriate prism-type reflector 4t) and reflector 42 through respective side apertures 44 and 46 in the platen 16. Mirrors 48 and 50 are provided on the platen 16 to reflect the light 'beams from the reflectors 40 and 42 down the respective edges of the film strip 14. l

The rotatable reflector member 12 is driven by la driv sensor 56 reads the recordings on the member 54, and it produces electric pulses as the member 54 rotates. These electricpulses are indicative of the 'angular movement of Therefore, as the rotatable reflector l2 is rotated by the drive motor 51, it causes the laser beam from the laser light source 10 to be recurrently scanned across the film strip 14. At the same time, the synchronizing pulses from the sensor 56 are applied to the light modulator 38, so that a series vof recordings R (FIGURE 4) are recorded at each edge of the film strip 14, the recordings R being in respective alignment with respective ones of the transverse tracks formed by the transverse scanning of the laser light beam, as described above. The recordings R" are used subsequently, as will be described, for controlling the registration of the scanning beam during the reproduction process in the system of FGURE 5..

Many of the components used in the reproducing system of FIGURE 5 are similar to those'used in the recording system of FIGURES l and 3, and such components have beendesignated by the same numbers.

In the reproducing system of FIGURE `5, the laser iight beam from 'the source lll is directed through the halfsilvered mirror 36 and through the lens 18 to the surface of the rotatable reflector 12. For reproducing purposes, the laser light beam is unmodulated, and it is recurrently scanned across the lm strip 14. The scanned laser light beam must be maintained in registry with the transverse recording tracks on the film strip, as recorded by the system of FIGURES 1 and 3, so that the information contained in these tracksmay be reproduced.`

As the lightbeam is scanned across the film strip 14 in the reproducing system of FIGURE 5, it is modulated in accordance with the recordings on the film strip. The resulting modulated beam is directed through the platen 16 to an appropriate photo-cell (not shown) so that the recording may be converted into corresponding electrical signals for subsequent utilization. y The auxiliary light beam produced by the half-silvered mirror 36 isagain reflected tothe edges ot` the film strip 14 as two distinct beams. The reflected beams are modulated by the recordings R on the edges of the film strip, and the resulting modulated light beams are passed through a pair of optical fibers 6i) and 62 to corresponding photo-cells 64 and 66. The photo-cells producecorrespending electrical pulses in response to the modulated light beams directed thereto.

The optical fibers as is is known to the art,.are transparent fibers which are used generally to conduct light f along selected paths. The vliber may be flexible to conduct the light through tortuous channels. A description of optical fibers may be found in the McGraw-Hill Encyclopediaof Science and Technology, published 1960,'

by the McGraw-Hill Book Co., Inc.

The pulses from the photo-cell 66,- for example, are amplified in an amplifier 68 and applied to a phase detector 70. The synchronizing pulses from the sensor 56, as amplified bythe amplifier 58, are also applied to the phase detector 70, and the resulting phase error signal is applied to a skew control 72. The skew control 72 may be any appropriate solenoid type controhand it mechanically coacts with the edges of the lm strip 14 to realign the film should skewing occur.

The presence of skewing of the film strip 14 is evidenced by a phase displacement between the modulated light signals passed by the optical fiber 62 and the synchronizing pulses from the amplifier 5S. So long as these signals are in phase, the tllm strip 14 is being drawn true along its path. However, any skewing of the film strip produces an out-of-phase condition, and the result- `ing phase error signal from the phase detector 70 causes the skew control 72 to correct the condition..

The pulses from the` photo-cell 64 are amplified in an amplifier 76 and applied to a phase detector 78. The pulses from the amplifier S8 are also applied to the phase detector 78 and the phase error signal from the phase detector is applied to a usual type of motor speed control system 80. i

The speed control system 80 controls the speed of the recording medium drive motor 82 which, for example, is coupled to a drive capstan 84. The drive capstan 254 draws the recording film strip M along its predetermined path in any known manner. The recording medium drive'rnotor 32 may, of course, be directly coupled to any other type of drive mechanism for the lm strip i4.

it is most important during the reproduction process that the transversely scanned laser light beam is maintained in registry with the transverse recordings on the film strip. controlled, so that should the speed of the film strip change to cause the laser light beam to become misaligned with the transverse recordings on the filtri. the resulting phase error signal from the phase detector 78 causes thc speed of the film strip to be varied in a manner to couipensate for such misregistration.

Therefore, the reproducing system of FIGURE 5 includes appropriate'controls to assure that the film strip is driven at the proper speed and without skewing, so that exact registry between the scanning light beam and the transverse recordings on the film strip is assured.

The invention provides, therefore, an improved optical recording-system which is capable of high speed, high density recording for signals through a wide frequency range.

The improved system of the invention is controlled so that the recordings may be made with precision and exactness, and so that subsequent reproduction may be made with exact registration between the scanning beam and the transverse-recordings on the iiim strip.

While aparticular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the claims to cover such modifications which fall within the spirit and scope of the invention.

What is claimed is:

l. in combination: a light source for producing light in the form of a high intensity iight beam; means for moving a photographic film strip along a particular path; means disposed in. the path of said light beam for directing said light beam to said-film strip; means coupled to said directing means for causing said directing means to scan said light beam transversely across said film strip; platen means tor supporting said film strip; microineter adjustment means mechanically coupled to said platen to adjust the position of said platen towards and away from said directing means; and ambient condition sensing control means coupled to said micrometer adjustment means for causing said platen to shift so as to compensate for changes in thickness of said film strip due tov variations in ambient conditions.

2. The. combination defined in claim l and which in cludes: a lens interposed between said light source and said directing means for focusing said light beam in the piane of said film strip; further micrometer adjustment means mechanically coupled to said lens for adjusting the position of said lens towards and away from said directing means; and in which said ambient condition sensing control'means is coupled to said `further micrometer adjustment means for causing said lens to maintain said light beam focused in the plane of said film strip in the presence of variations in the effective position of said piane due to varying ambient conditions.

3. in combination: a light source for producing light in the form of a rst high intensity light beam; means for moving a photographic film strip along a particular path; a rotatable-reflecting member having a polygonal peripheral configuration disposed in the path of said light beam for reflecting said lightbeam to said film strip;

The reproducing system of FIGURE 5 is lll) means coupled to said reflecting member for imparting rotational motion thereto so as rccurrcntly to scan said tight beam transversely across said tilm strip; a synchro nizing member coupled to said rotatable reficctingiiieinber for producing synchronizing signals indicative of the angular positions of said rellecting member; means for producing a second light beam; means for directing said second .light beam to at least one edge ot' said film strip; and modulating means disposed in the patti of said second light beam and coupled to said synchronizing member, said modulating means being responsive to said Synchronizing signals tor causing recordings to be made on the edge of said film strip indicative of successive transverse paths of said first light beam as said first beam is scanned transversely across said filtri strip.

4. in combination: a light source for producing light in thc forni of a high intensity light beam; means for drawing a photographic film strip along a particular path, said lilin strip having recordings at the edges thereof in registry with successive transverse recording tracks on the film strip; a rotatable retlecting member having a polygonal peripheral surface and disposed in the path of said light beam for directing said light beam to Said film strip; means coupled to said reflecting member for imparting rotational movement thereto so as to cause said reflecting member to scan said light beam transversely across said film strip; means for producing a second light beam; further reflecting means positioned in the path of said second light beam for causing said second light beam to be reflected as a pair of beams on the edges of said film strip `and be modulated by the recordings at said edges; photoelectric cell means disposed in the paths of at least one of the modulated pair of beams and responsive thereto for producing corresponding electrical signals; and control means coupled. to said photoiceil' v motion thereto to cause said light beam to be recurrently scanned transversely across said film strip:.and vacuumactuated platen means for supporting said film strip in thc path of said transversely scanned light beam, including synchronizing means including afmagnetie member coupled to said rotatably mounted reflectingl member for producing synchronizing pulses indicative of the angular positions of said reflecting member; means for producing a second light beam; reflecting means disposed in the path ofvsaid second light beam i'or directing Asaid second light beam to theedges of said film strip; and light modulating means disposed in the path of said sec- .ond light beam and coupled to said synchronizing means; said modulating means being responsive to said synchronizing pulses produced by said synchronizing means to provide recordings on the edges of said film strip in registry with successive paths across said .film strip of said transversely scanned light beam.

References Cited in the file of this patent UNI'IED STATES PATENTS 2,787,214 Halahan et al. Apr. 2, 1957 2,898,176 McNaney .'Aug. 4, 1959 2,945,414 Blackstone July 19', 1960 2,999,436 Faulhaber Sept. 12, 1961 3.008.792 Cox Nov; 14, 1961 3,059,111 Boyle et al. Oct. 16, 1962 

1. IN COMBINATION: A LIGHT SOURCE FOR PRODUCING LIGHT IN THE FORM OF A HIGH INTENSITY LIGHT BEAM; MEANS FOR MOVING A PHOTOGRAPHIC FILM STRIP ALONG A PARTICULAR PATH; MEANS DISPOSED IN THE PATH OF SAID LIGHT BEAM FOR DIRECTING SAID LIGHT BEAM TO SAID FILM STRIP; MEANS COUPLED TO SAID DIRECTING MEANS FOR CAUSING SAID DIRECTING MEANS TO SCAN SAID LIGHT BEAM TRANSVERSELY ACROSS SAID FILM STRIP; PLATEN MEANS FOR SUPPORTING SAID FILM STRIP; MICROMETER ADJUSTMENT MEANS MECHANICALLY COUPLED TO SAID PLATEN TO ADJUST THE POSITION OF SAID PLATEN TOWARDS AND AWAY FROM SAID DIRECTING MEANS; AND AMBIENT CONDITION SENSING CONTROL MEANS COUPLED TO SAID MICROMETER ADJUSTMENT MEANS FOR CAUSING SAID PLATEN TO SHIFT SO AS TO COMPENSATE FOR CHANGES IN THICKNESS OF SAID FILM STRIP DUE TO VARIATIONS IN AMBIENT CONDITIONS. 